Conventional sensing technologies employed to determine the angle or angular displacement of a shaft of a motion control system include encoders, resolvers, and potentiometers. These sensing technologies are readily available, however, they require a fair amount of space to connect to the shaft. Further, these technologies can also be quite costly when implemented in a high volume product.
However, less costly prior art technology for measuring angular displacement of a shaft of a motion control system is available. This technology utilizes three Hall effect sensors mounted in a brushless DC motor to provide motor commutation signals. The three Hall effect sensor signals are indicative of three electrical angles of the motor rotor. Brushless motors produce motion according to the commutation logic based on these three electrical angles of the motor rotor measured by the Hall effect sensors.
The use of the Hall effect sensors in conjunction with a brushless motor provides a much more cost effective method of sensing the angular displacement of the shaft of a motion control system. The Hall effect technology also employs no moving parts resulting in higher reliability. The disadvantage of using Hall effect sensors in the brushless motor to sense angular displacement of a shaft of a motion control system, is that the angular measurement resolution is typically lower than that of an encoder, resolver, or potentiometer.
Additionally, known techniques of processing Hall effect sensor signals to provide an angle or angular displacement have included the use of an index position signal to track the number of shaft resolutions. The index position requires an additional sensor and additional processing hardware. The additional components increase the cost and complexity of the angle sensing system for applications which only require a relative angle measurement and a continuous angular output. The resolution of angle measurement is also limited by the resolution of the hardware devices. In view of the above, it is apparent that there exists a need for a system and method for sensing the angle and angular displacement of a shaft using low cost Hall effect sensors with improved resolution.